Configuration

The software of RCHv2 is growing slowly by surely :) After many thoughts, I decided that the configuration of the mixers will be done through "xml" like commands. "xml" is a structured language to specify datas, very useful when datas start to be complex and a lot imbricated. And this is the case with the software of the radio, because I wanted it to be powerfull and generic enough to allow users to do powerfull mix without headaches. If I fail, then I will provide 'aspirin' to anyone who wants to build and use an RCH system :)

So, given that there is a lot to do to reach that objective, I am trying to proceed small steps by small steps, which is not always obvious. My next step is to allow the configuration of RCHv2 from a PC with an XML configuration file.
You should say "ok, but what's the benefit of that ? " answer is: to be able to provide almost any kind of parameters to the radio, thus to allow to program anything. You could argue that "xml" has a cost, and that it takes SRAM ressources as well as CPU. Answer: Yes that's not wrong, but I 'll give a try on an AVR8bits, and I am pretty sure that CPU resources will be very small, and that there will be still sufficient SRAM memory to proceed.
Once config from XML will work, it will be a great step forward.
I have also planned to add a second avr644P for LCD and keyboard handling.

Please comment, if you think what I am doing is stupid, obvious, or bad way, thanks in advance :)

Some Spectrum measurements

Last monday I had the opportunity with friends to do some measurements of spectrum on various 2.4Ghz modules.
The initial intention was to measure the difference between 2.4Ghz antennas, but the environment (in a shop) reveals that it was impossible.
So, no results about the antenna efficiency, but we could observe the spectrum of various transmitter. Thanks to flash-rc who makes this possible to test different transmitter from various vendors.
First, here is the spectrum print for the Xbee module that is used in some home made RC. You can see that the spectrum is not very sharp around the 2.46Ghz channel, and there are many harmonic around.



Then we tried Assan module. Very interesting. Its Spectrum is very sharp and neat. It uses DHSS technology with two channels simultaneously as Spectrum. It looks clean.





Then we tried several transmitter together to compare their Spectrum. The picture below shows Assan, Spektrum and Xbee. The Xbee transmit only on one single channel at a time.



Finally, we tried two Futaba transmitters simultaneously. On the picture you can see that they use the entire spectrum 2.4Ghz. They use the FHSS technology. Don't be afraid by this picture, the spectrum here is remanent and it does not mean that the radio continuously emit on all these channels at the same time.



In conclusion of all this, if I have to buy 2.4Ghz module, I would seriously investigate Assan as their Spectrum looks very clean, which make feel confident in it. But of course it is just one aspect. In addition, it looks that the DHSS technology is more suited to RC because it seems to be more robust against jamming. DHSS techology is based on CDMA, made for the Army for Missile guidance and comms. More info on DSS techno here. FHSS primarly purpose is communication crypting for army to prevent comms hijacking. [edit] But it looks that FHSS used by Futaba is not exactly same as FHSS used by the army. Subject is complex. There is an interesting thread about this on rcgroups

Transmitter case alu prototype

The transmitter case is almost finished. This is a prototype made with alumininium and epoxy plate (printed ciruit plate). If someone is interested, I can explain in another post how I built it. From the initial drawing, there have been some changes, such as dimensions.
But it is close to what was designed with Styro , except the round corners.

Knob unders the sticks are use both as trims, and as input for the lcd interface. It is planned also to add encoding wheel.
Stick are those of a Futaba FC18 with their trims removed. Mechanical trims under the sticks have finally little use, so they have been replaced by kind of "auto-trim" or preferably what I call "obo" trim.

Sides where hands hold the radio, are rounded. It is more comfortable to hold the radio, and to move the hands near the stick.

This case is mainly for pilots who use inches on (pouces dessus).
The display is a classical graphical lcd 128x64 and it sits between the stick as there is not enough space above, due to the compacity of the case.

Overall weight of the case is reasonable and should be fine when electronic and batteries will be in.


To make a size comparison with the Futaba T12Z, the case is larger but less long, and thiner than the 12Z. It feels also very comfortable in hands compared to the 12Z.

Transmitter box styro prototypes

After drawings, it is time to make some box in styro, to better feel the shape and how it will fit in hands. I made several trials. It's not easy to find the perfect balance betweeb size, shape, sexy look, good ergonomy, light weight, etc... The prototype will not be perfect for sure, but it will benefit to check the dimensions, size, and ergonomy. Let's hope it will work like that, it would be nice to keep the box small if possible.

Differential mix variable rate

Another video to show how Aileron differential is reduced when using butterfly mix such as it can be in a competition glider. Very useful to keep turning while airbrakes are fully out.

Atmega328

Another interesting chip as a possible improvement of the Atmega168. Same pins, but more SRAM (2k) and more Flash(32k). It should fit in the Arduino easily.
Nice evolution to the atmega168, but has some drawbacks:
- the bootloader from Arduino do not work from scratch,
- the tools avrdude, gcc-avr do not know the 328.
[edit] correction:
- the last version of Arduino (0013) supported the 328: It provides avr-dude with the right conf file, and the bootloader source file and Makefile have been updated for the 328,
- I tried to define m328p as a target for avr-gcc, and it works also.

So no more reasons not to replace your 168 on the Arduino by a 328!

Unigen module

Today I received a new toy :)
Could be a good replacement for the XBee module, less expensive more flexible, approximately the same size than the Maxstream Xbee pro.